If you cast Nemesis Trap for , you may still target any attacking creature, not just the white attacking creature.

3/1/2010

An “attacking creature” is one that has been declared as an attacker this combat, or one that was put onto the battlefield attacking this combat. Unless that creature leaves combat, it continues to be an attacking creature through the end of combat step, even if the player it was attacking has left the game, or the planeswalker it was attacking has left combat.

3/1/2010

If you cast Nemesis Trap during your opponent’s declare attackers step, you’ll put the token onto the battlefield before the declare blockers step begins and you can block with it this combat. If you cast Nemesis Trap later in the combat phase a, you won’t be able to block with the token.

3/1/2010

The token you put onto the battlefield copies exactly what was printed on the exiled creature and nothing more (unless it was copying something else or it was a token; see below). It doesn’t copy whether the exiled creature was tapped or untapped, whether it had any counters on it or Auras attached to it, or any non-copy effects that changed its power, toughness, types, color, or so on. For example, if Nemesis Trap targets an animated Celestial Colonnade, the token you put onto the battlefield will be a Celestial Colonnade that’s just a land. (Because of this, Nemesis Trap has received minor errata to specify that you put a token, not a “creature token,” onto the battlefield.)

3/1/2010

If the exiled creature was copying something else (for example, if it was a Jwari Shapeshifter), then your token enters the battlefield as a copy of whatever the exiled creature was copying.

3/1/2010

If the exiled creature was a token, your token copies the original characteristics of that token as stated by the effect that put it onto the battlefield.

3/1/2010

If the exiled creature has in its mana cost (such as Protean Hydra), X is considered to be zero.

3/1/2010

Any enters-the-battlefield abilities of the exiled creature will trigger when the token is put onto the battlefield. Any “as [this creature] enters the battlefield” or “[this creature] enters the battlefield with” abilities of the chosen creature will also work.

3/1/2010

If the targeted creature is an illegal target by the time Nemesis Trap resolves, the entire spell doesn’t resolve. You won’t get a token.